This invention relates to hydraulic actuation systems and in particular hydraulic actuation systems for automated transmission systems.
In automated transmission systems of, for example, the type disclosed in WO97/05410 or WO97/40300, whose content is expressly incorporated in the disclosure content of the present application, fluid pressure actuators are used to control actuation of a clutch actuator mechanism and/or a gear engaging mechanism. In accordance with WO97/05410, separate control valves are used to control the clutch actuator mechanism and the gear engaging mechanism.
WO97/40300 discloses a hydraulic actuation system in which a main control valve controls both the clutch actuation mechanism and, together with secondary valves, shift and select actuators of a gear engaging mechanism. The use of a single main control valve in this manner reduces the number of components, providing savings in the overall size and cost of the system. The design of the master control valve is however significantly more complicated, which reduces the cost savings.
The use of a main control valve to control both the clutch and gear engagement actuator requires that the gear engagement actuator is connected to a source of hydraulic fluid under pressure when the clutch actuator is connected to the source of hydraulic fluid under pressure, the gear engagement actuator being isolated from the source of hydraulic fluid under pressure only when the clutch actuator is connected to a reservoir.
When the transmission system utilises a clutch which is maintained in engagement by mechanical spring means, the clutch being disengaged by the application of fluid pressure to a clutch actuator, this form of hydraulic actuation system permits the clutch actuator and the gear engagement actuator to be depressurised when the vehicle is in gear with the clutch engaged, thereby reducing the number of potential leakage points when the actuation system is not in use.
However if the transmission system utilises an active clutch, which is maintained in engagement by the application of fluid pressure to a clutch actuator, the clutch being disengaged by connection of the clutch actuator to a reservoir, the hydraulic actuation system of the type known will require the gear engagement actuator to be pressurised whenever to clutch is engaged, thereby increasing the number of potential leakage points.
According to one aspect of the present invention a hydraulic actuation system for an automated transmission system including an active clutch comprises:
a hydraulic clutch actuator for controlling engagement of an active clutch;
a gear engagement actuator for controlling engagement of a gear; a source of hydraulic fluid under pressure;
a hydraulic fluid reservoir;
a main control valve for selectively connecting the hydraulic clutch actuator and the gear engagement actuator to the source of hydraulic fluid under pressure or to the reservoir; and
an isolation valve for isolating the gear engagement actuator from the main control valve, when the clutch actuator is connected to the source of hydraulic fluid under pressure;
the clutch actuator causing the clutch to engage when connected to the source of hydraulic fluid under pressure and causing the clutch to disengage when connected to the reservoir.
With the hydraulic actuation system disclosed above, the isolation valve will disconnect the gear engagement actuator from the source of hydraulic fluid under pressure when the clutch actuator is pressurised and the clutch engaged. The number of potential leakage points is thereby reduced.
According to a further aspect of the present invention a hydraulic actuation system for an automated twin clutch transmission system having:
a first active clutch for transmitting torque via a first set of gears;
a second active clutch for transmitting torque via a second set of gears; said hydraulic actuation system comprising;
a source of hydraulic fluid under pressure;
a hydraulic fluid reservoir;
a first hydraulic clutch actuator for controlling engagement of said first active clutch;
a second hydraulic clutch actuator for controlling engagement of said second active clutch;
a first gear engagement actuator for controlling engagement of one if said first set of gears;
a second gear engagement actuator for controlling engagement of one of said second set of gears;
a first main control valve for selectively connecting the first clutch actuator and the first gear engagement actuator to the source of hydraulic fluid under pressure or to the reservoir; and
a first isolation valve for isolating the first gear engagement actuator from the first main control valve, when the first clutch actuator is connected to the source of hydraulic fluid under pressure;
a second main control valve for selectively connecting the second clutch actuator and the second gear engagement actuator to the source of hydraulic fluid under pressure or to the reservoir; and
a second isolation valve for isolating the second gear engagement actuator from the second main control valve, when the second clutch actuator is connected to the source of hydraulic fluid under pressure;
the first and second main control valves being connected to the source of hydraulic fluid under pressure and to the reservoir in parallel. With the twin clutch transmission system disclosed above the hydraulic control system permits a gear associated with one clutch to be engaged while that clutch is disengaged and the other clutch is engaged. Said one clutch may then be engaged as said other clutch is disengaged, in order to engage a new gear. The engagement of one clutch and disengagement of the other clutch may be controlled so that the torque transmitted is maintained constant and a smooth change is achieved.
The use of parallel hydraulic actuation systems permits one clutch and the gears associated therewith to be used, even though the other clutch/actuation system may be inoperative, so that the vehicle may be driven, albeit in a restricted mode.